Support: Rope Selection: Rope Cores The primary function of the rope's core is to serve as the foundation for the strands - to keep the rope round and the strands properly positioned during operation. Your choice of core will have an effect upon the rope's performance. Three types of cores are most commonly used: Fiber core: polypropylene is standard, but either natural fiber or other man-made fibers are available on special request. Independent Wire Rope Core: literally an independent wire rope with strands and a core, called IWRC. Most wire ropes made with steel core use an IWRC. Strand core: a strand made of wires. Typically, strand cores are used in utility cables only.